1. Field of the Invention
The present invention relates to a method of fabricating an electron source, a method of fabricating an image forming apparatus using the electron source, and a forming method.
2. Related Background Art
Conventionally, electron-emitting devices are mainly classified into two types: thermionic and cold cathode elements. Known examples of the cold cathode are field emission type electron-emitting devices (to be referred to as FE type electron-emitting devices hereinafter), metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter), and surface-conduction type electron-emitting devices.
Known examples of the FE type electron-emitting devices are disclosed in W. P. Dyke and W. W. Dolan, "Field Emission", Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, "Physical Properties of Thin-Film Field Emission Cathodes with Molybdenium Cones", J. Appl. Phys., 47, 5248 (1976).
A known example of the MIM type electron-emitting devices is disclosed in C. A. Mead, "Operation of Tunnel-Emission Devices", J. Appl. Phys., 32, 646 (1961).
An example of the structure and fabrication method of the surface-conduction type electron-emitting devices is disclosed in Japanese Patent Application Laid-Open No. 7-235255. This application also discloses an example of an electron source constituted by arranging many surface-conduction type electron-emitting devices on a substrate, and an image forming apparatus using this electron source.
The surface-conduction type electron-emitting device will be briefly explained. FIG. 10 is a schematic (plan) view showing the structure of a surface-conduction type electron-emitting device. A pair of device electrodes 2 and 3 are arranged on a substrate 1 to face each other, and a conductive film 4 is formed to be connected to both the device electrodes. An electron emitting region 5 is formed in the conductive film. In FIG. 10, the electron emitting region 5 is straight near the center between the device electrodes. In practice, the electron emitting region 5 may be bent or formed close to one device electrode.
Japanese Patent Application Laid-Open No. 7-235255 further discloses a more detailed structure of the surface-conduction type electron-emitting device. FIG. 11 schematically shows the section of the electron-emitting device. A gap is formed in part of the conductive film 4, and a film 6 containing carbon as a principal ingredient is formed around the gap.
As shown in FIG. 11, the film 6 containing carbon as a principal ingredient is formed in at least the gap of the conductive film 4.
The gap in part of the conductive film is formed by applying a voltage between the device electrodes 2 and 3 and flowing a current through the conductive film 4. The process of flowing a current and forming a gap in the conductive film is called an "energization forming process" or simply "forming process". The voltage applied in the "forming" process is a pulse voltage or the like, as disclosed in Japanese Patent Application Laid-Open No. 7-235255. Japanese Patent Application Laid-Open Nos. 7-320631 and 7-176265 disclose methods of performing this forming process in forming a plurality of electron-emitting devices.
Japanese Patent Application Laid-Open Nos. 6-12997 and 9-298029 disclose that the forming process is done for a conductive film made of a metal oxide in an atmosphere containing a reducing gas such as hydrogen gas, thereby reducing power necessary for the forming process and more effectively forming the gap.
The process of forming the film 6 containing carbon as a principal ingredient is called an "energization activation" process or simply "activation" process. The activation process is executed by setting, e.g., an electron-emitting device having undergone the forming process in an organic-gas-containing atmosphere and repeatedly applying a pulse voltage between a pair of device electrodes.
Japanese Patent Application Laid-Open Nos. 9-73859 and 9-134666 disclose methods of performing the activation process for a plurality of electron-emitting devices.
The present applicant proposed an electron source formed by arranging many electron-emitting devices on a substrate and wiring them in a matrix as schematically shown in FIG. 12. The above-mentioned patent applications field by the present applicant also disclose electron sources having this structure. For descriptive convenience, a wiring 12 extending in the lateral direction in FIG. 12 will be referred to as an x- or row-direction wiring 12, and a wiring 13 extending in the longitudinal direction will be referred to as a y- or column-direction wiring. At an intersection of the x- and y-direction wirings, an interlayer insulating layer (not shown) is formed to electrically insulate from each other.